The present invention is directed to multicomponent fibers. More particularly, the present invention is directed to multicomponent fibers including, but limited to, bicomponent polymer fibers, wherein at least a portion of the exposed surface of the fiber comprises poly(ethylene oxide), desirably a grafted poly(ethylene oxide). Such fibers can be used to manufacture nonwoven webs that can be used as components in medical and health care related items, wipes and personal care absorbent articles such as diapers, training pants, incontinence garments, sanitary napkins, pantiliners, bandages and the like.
Disposable personal care products such as pantiliners, diapers, tampons etc. are a great convenience. Such products provide the benefit of one time, sanitary use and are convenient because they are easy to use. However, disposal of many such products is a concern due to limited landfill space. Incineration of such products is not desirable because of increasing concerns about air quality and the costs and difficulty associated with separating such products from other disposed, non-incineratable articles. Consequently, there is a need for disposable products, which may be quickly and conveniently disposed of without dumping or incineration.
It has been proposed to dispose of such products in municipal and private sewage systems. Ideally, such products would be flushable and degradable in conventional sewage systems. Products suited for disposal in sewage systems and that can be flushed down conventional toilets, in conventional tap water, are termed xe2x80x9cflushablexe2x80x9d herein. Disposal by flushing provides the additional benefit of providing a simple, convenient and sanitary means of disposal. In order to be commercially desirable, personal care products must have sufficient strength under the environmental conditions in which they will be used and be able to withstand the temperature and humidity conditions encountered during use and storage yet lose integrity upon contact with water in the toilet. Desirably, such products can be manufactured economically using conventional manufacturing equipment and methods. Therefore, a water-disintegratable material which is thermally processable into fibers and having mechanical integrity when dry is desirable for making nonwoven webs that can be used as components in such care articles.
Due to its unique interaction with water and body fluids, poly(ethylene oxide) (hereinafter PEO) is currently being considered as a component material in fibers and flushable products. PEO, xe2x80x94(CH2CH2O)nxe2x80x94,
is a commercially available water-soluble polymer that can be produced from the ring opening polymerization of ethylene oxide, 
Because of its water-soluble properties, PEO is desirable for flushable applications. However, there is a dilemma in utilizing PEO in the fiber-making processes. PEO resins of low molecular weights, for example 200,000 grams per mol (hereinafter abbreviated as g/mol) have desirable melt viscosity and melt pressure properties for extrusion processing, but cannot be processed into fibers due to their low melt elasticities and low melt strengths. PEO resins of higher molecular weights, for example greater than 1,000,000 g/mol, have melt viscosities that are too high for fiber-spinning processes. These properties make conventional PEO difficult to process into fibers using conventional fiber-making processes.
Conventional PEO resins that are melt extruded from spinning plates and fiber spinning lines resist drawing and are easily broken. Conventional PEO resins do not readily form fibers using conventional melt fiber-making processes. As used herein, fibers are defined as filaments or threads or filament-like or thread-like structures with diameters of about 100 microns and less. Conventional PEO resins can only be melt processed into strands with diameters in the range of several millimeters. Therefore, PEO compositions with melt viscosities appropriate for processing fibers and with greater melt elasticities and melt strengths are desired.
In the personal care industry, flushable melt-spun fibers are desired for commercial applications. It has not been possible to melt process fibers from conventional PEO compositions using conventional fiber making techniques such as melt spinning. Melt processing techniques are more desirable than solution casting because melt-processing techniques are more efficient and economical. Melt processing of fibers is needed for commercial viability. Conventional compositions cannot be extruded into a melt with adequate melt strength and elasticity to allow attenuation of fibers. Presently, fibers cannot be produced from conventional PEO resins by melting spinning.
Thus, currently available PEO resins are not practical for melt extrusion into fibers or for personal care applications. What is needed in the art, therefore, is a means to overcome the difficulties in melt processing of PEO resins so that PEO resins can be formed easily and efficiently into fibers for later use as components in flushable, personal care products. It would also be desirable to provide water-responsive fiber compositions and structures that can be readily processed by melt spinning at high jet stretch ratios yet have desirable dry mechanical properties.
It has been discovered that water-responsive multicomponent fibers comprising at least two components: (1) a water-responsive modified or an unmodified PEO and (2) a thermoplastic, polymer that is not PEO, can be manufactured at higher jet stretch ratios compared to PEO alone. These water-responsive fibers can be made using conventional processing methods from commercially available PEO resins when modified or grafted with xcex1,xcex2-unsaturated moieties to produce a graft copolymer of the PEO resin and the selected xcex1,xcex2-unsaturated moiety or moieties. When a water-responsive PEO forms an exposed surface on at least a portion of the multicomponent fiber and the fibers are used to form a nonwoven web, the nonwoven web is water responsive. Advantageously, when such a web is exposed to water, such as ordinary tap water contained in a toilet bowl, the fiber to fiber bonds of the PEO exterior portions degrade and the fibrous nonwoven web will lose its integrity and break apart into smaller pieces or individual fibers that are ultimately flushable.
The non-PEO, thermoplastic component of the fibers should be water-responsive, desirably, water-weakenable and more desirably water-soluble. Desirably, the thermoplastic, non-PEO component of the multicomponent fiber is capable of being extruded and can be readily formed into fibers using conventional fiber making equipment and processes and aids in the processing of the multicomponent fibers. The non-PEO component of the multicomponent fibers can be any thermoplastic that is capable of being melt processed into fibers. Nonlimiting examples of thermoplastic polymers that can be used as the non-PEO component in the multicomponent fibers of the present invention include, but are not limited to, polyolefins and polyesters. If desired, the multicomponent fibers of the present invention can also include additional components including, but not limited to, other optional layers, polymers and additives.
The multicomponent fibers of the present invention may be manufactured in a number of forms including, but not limited to, fibers having sheath/core and side-by-side configurations. Desirably, the PEO component of the multicomponent fibers is distributed on an exterior surface of the fibers in a sufficient quantity to allow PEO/PEO bonding between fibers. More desirably, the exterior surface of the fibers is composed of a majority of PEO, i.e. greater than 50 percent by cross-sectional area. The multicomponent fibers may include other components, additives or layers and the individual components themselves may comprise additional additives, colorants and the like.
The PEO resins useful for the present invention include, but are not limited to, water-responsive PEO resins including water-disintegratable, water-weakenable, and water-soluble PEO resins. Grafted PEO compositions are particularly suitable for the present invention, particularly PEO resins grafted with polar moieties. Grafted PEO resins provide a balance between mechanical and physical properties and processing properties. Suggested polar moieties include a variety of polar vinyl monomers, oligomers, and/or polymers, as well as, any other reactive chemical species, which is capable of covalent bonding with the PEO resin. Suggested polar vinyl monomers include, but are not limited to, 2-hydroxyethyl methacrylate and poly(ethylene glycol) methacrylates such as poly(ethylene glycol) ethyl ether methacrylate.
The present invention discloses a broad class of multicomponent fibers comprising a core polymer that is not PEO and a water-soluble exterior portion, sheath or coating of PEO. Due to the water-soluble nature of PEO, it is desirable to make a multicomponent fiber structure, which has an exterior portion comprising PEO. One desirable embodiment of the present invention includes bicomponent fibers having a concentric and eccentric structure in a sheath/core configuration. The bicomponent fibers are comprised of two main components: a fiber-grade core component and a PEO sheath component. The non-PEO component of the present invention can be any thermoplastic polymer capable of being spun into fibers. Suggested non-PEO components include, but are not limited to, polyolefins and polylactides.
The present invention is further directed to nonwoven webs comprising the above-described multicomponent fibers. In one desired embodiment, the nonwoven webs are water-responsive and flushable.